1. Field of the Invention
The invention relates in general to a color adjusting apparatus and method for a light source. More particularly, the invention relates to a color adjusting apparatus and method of use for a light source of an optical scan module.
2. Related Art of the Invention
As image input, operation and processing have caused popular interest, the scanner becomes a basic accessory for many computer users. Through the scanner, text or graphs in documents, magazines, books or pictures can be scanned and input into a computer for further processing. The platform scanner is the most common type among various kinds of scanners. In the platform scanner, the scan module, installed under a transparent platform, can be pulled back and forth to scan the document on the transparent platform. The scan module itself does not have a driving mechanism, so the driving mechanism such as a motor, gear, and belt are required. While using the platform scanner to scan a document, the document has to be disposed on the transparent platform and covered with a lid, which presses the document down on the transparent platform.
The conventional scan module 700 of an optical scanner (referring to FIG. 1) includes a light source 100, a mirror set 400, a lens set 500 and an optical detector such as charge-coupled device (CCD) 600. While performing a scan, the light source (such as a light tube) 100 radiates on the document 200 disposed on the light transparent board 300 (which is the transparent platform). An imaging light 110 is obtained via reflection (where the light source 100 is located underneath the light transparent board 300) or transmission (where the light source 100 is located over the light transparent board 300). The mirror set 400 is an assembly of multiple mirrors 401, 402, 403 and is located along the optical path of the imaging light 110. The image of the document 200 directed to the mirror set 400 is reflected to the lens set 500 thereby. Through the lens set 500, the imaging light 110 of the document 200 is incident and displayed on the charge-coupled device 600.
The light source 100 of the optical scan module 700 is a very important device for the whole optical system. The light emitted by the light source 100 generates various intensities according to the frequency thereof. Through the function of the charge-coupled device 600, for example, after inspection of modulation transfer function (MTF), a certain degree of color deviation often results. Therefore, compensation and correction in a firmware for each scan step is required to obtain the correct color. This is very costly and time consuming.
The function of the lens set 500 is to display the imaging light 100 on the charge-coupled device 600. That is, the light signal collected by the lens set 500 is the material source that all the subsequent devices are processing. Therefore, the correctness of the light signal is crucial. Generally speaking, as shown in FIG. 2, the lens set 500 is a composite signal lens consisting of a plurality of lenses, for example, the lenses 510, 520 and 530 as shown in FIG. 1 and installed in the lens holder 710. Using lenses with different materials or curvatures, the aberration caused by a single lens is corrected. However, as the wavelength transmission for the lenses 510, 520 and 530 is different, inconsistent output intensities in the primary colors red, green and blue of the charge-couple device 600 results.
Further, the charge-coupled device 600 comprises thousands of optoelectronic diodes (pixels) arranged in straight lines. Each optoelectronic diode comprises three detectors to receive the red, green and blue color light signals, respectively. In the scanning operation, the charge-coupled device 600 outputs analog red, green and blue electronic signals for the light received in each sequence. By analog-to-digital conversion, the converted signals are then transmitted to the subsequent devices for processing. The detectors of the charge-coupled device 600 do not detect only one single primary color signal. Therefore, frequency response of mutual interference between color signals occurs. The light sensitivity of the charge-coupled device 600 is degraded due to different light sensitivity generated for different colors, increased scan moving speed of the charge-coupled device 600 and decrease of exposure amount. Accordingly, inconsistent output intensities for red, green and blue light are generated by the charge-coupled device 600.